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Testing the Theory of Relativity
HD 456 wrote to us with an MSNBC story about the new observatories that are starting to come online for the purpose of gravity wave research. One is located outside New Orleans, the other in Washington State, the facilities will shoot lasers down 2.5 mile tunnels in an attempt to detect changes in gravity caused by black holes. Redundancy in facilities is being used to avoid having false background noise skew results. In addition to garnering more information on black holes, the scientists also hope to collect data concering the origin of matter.
I honest to god was speaking to a friend just yesterday about this very issue. I wanted to take a laser, shoot it several miles down a tunnel, and put a large magnet to answer the question "is light matter or energy"? Damn. Guess that's one less experiment for me to worry about. Freaky. Very freaky. Deja vu freaky.
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Its karma, Kramer.
Contary to the belief of Fred Moody (as pointed out by another reader) - merely observing a black hole will not create one. Only stupid people generate black holes. Fortunately those are kept between their two ears, and they are buried with them. Relax, Fred. Just don't go near stupid people - they have a tendancy to suck.
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How complex are these gravity waves going to be? To me, it seems that we're going to have to filter out the background noises (the redundancy seems to solve most, but not all, of that) and then try to see if the lasers were changed, and if so, by what and in what manner.
This seems to lend itself to the kind of distributed effort seen by seti@home - which does a lot of the same things (mainly filtering out background noise & analyzing for signals). On the other hand, it might not be quite so complex. I don't know if I'm giving up on detecting extraterrestrial life from my desktop just yet, but analyzing gravity waves would be a very fun thing to have my computer doing!
-Denor
I'm confused...
I thought Relativity described gravity in terms of warped space, not particle/waves.
"Reactionaries must be deprived of the right to voice their opinions; only the people have that right." - Mao
the facilities will shot lasers down 2.5 mile tunnels in an attempt to detect changes in gravity caused by black holes
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great... that's the kind of irresponsible science that goes on, eh? Putting black holes in 2.5 mile tunnels? Someone could get hurt!
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Of course, since everything in the universe interacts with everything else gravitationally, I ought to be able to deduce the superstructure of the universe and the motion of anything and everything in it by observing how my tea leaves settle on the bottom of my cup. With sensitive enough instruments, of course. My grandmother, for instance...
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"Convictions are more dangerous enemies of truth than lies."
Must be... they haven't done it yet, and they're already using the past tense of shoot!
See you, space cowboy...
There was a tiny mistake in dialect translation during the production of this story, they aren't working on any high-level theoretical physics down in Louisiana, they are working on something much more down to earth:
Backhoes.
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We cannot reason ourselves out of our basic irrationality. All we can do is learn the art of being irrational in a reasonable way.
Despite the suggestion to the contrary in the MSNBC story, gravitational waves have already been shown to exist. Joe Taylor and Joel Weisberg and their collaborators have demonstrated, using a binary star system, that Einstein's prediction of the rate at which energy is radiated away by accelerating masses is correct to better than one half of one percent. (This was the subject of the 1993 Nobel Prize in Physics, awarded to Taylor and Hulse.) These results also prove, for example, that gravitational waves travel at the same velocity as electromagnetic waves (ie, the speed of light, or 300,000 km/s).
LIGO is an exciting project that may open a whole new field of gravitational wave astronomy and directly probe the properties of such exotic objects as black holes and neutron stars. But it will do it using well-established physical principles.
A few months ago, I can't remember where I read it (maybe at /.), a gravitational experiment was set up to measure the effect that an eclipse had on large pendulums like the one in the Smithsonian. Cameras were placed to detect small variations in the pendulum's drift. As I recall, the very early preliminary data suggested that pendulums within the eclipse zone had variations, whereas those outside the zone did not. Now that would be something if true ! Has anyone heard anything more about this ?
Here's a usenet relativity FAQ if your interested in some info.
Here's some info on black holes too, while I'm at it.
Imagine if two probes (say Deep Space 8 and, er, 8.5) were equipped with lasers, so that they could shot at each other once they were outside major planetary influences. It's the only satisfactory solution (imho), because when you're on a planet there's no way you can say for sure that you've accounted for every microscopic movement. Granted, you've still got planet x out there somewhere, but what the heck. If the experiment was screwed up by the discovery of a new planet (or brown dwarf) I wouldn't complain too much.
Call me stupid, but hasn't the theory of Relativity been proven several times over? I remember at least one experiment involving atomic clocks on airplanes...
Friends don't let friends misuse the subjunctive.
I believe you can filter this kind of noise by having multiple detectors.
Several detectors 100s of miles apart will get the same signal from a distant black hole, but will get very different signals from local perturbations.
-Yarn - Rio Karma: Excellent
It increases the likelihood that the theoretical predictions are correct, BUT, I believe to really drive the point home we need to observe localised fluctuations in the S/T continuum.
Of course that's failed miserably so far
Its good to get excited tho
A large part of what makes LIGO interesting -- at least to those who believe it will work (see below) -- is the prospect of eventually being able to do some real astronomy with the thing; that is, the idea that particular astrophysical phenomena would send out unique and detectable gravitational wave signatures.
Kip Thorne, one of the world's bad-asses on this subject, I think talks about LIGO in his book from a few years back, Black Holes and Time Warps. Highly recommended if you're interested in this sort of thing.
Finally, it's worth pointing out (as the article did not) that there are real questions about the odds of getting useful data out of the thing. Admittedly, I trust Thorne's opinion on this a lot more than most, but there's definitely a pretty narrow zone where a) we'll detect lots of gravitational waves with LIGO and b) we wouldn't have detected them already. (If I'm not mistaken, there have been small-scale versions of LIGO done already.) I wish I could point you to a link on this, but I can't think of anything useful.
Just my two cents. :-)
Dueling singularities?
http://news2.thls.bbc.co.uk/hi/english/sci/tech/sp ecials/total_eclipse/newsid_415000/41527 3.stm
Is what you are referring to I think.
V. interesting stuff !
Life is just a bowl of All Bran - Small Faces
Your magnet will have no effect. Photons have no charge, and are uninfluenced by the other photons in the magnetic field. Energy does not exist apart from mass and vacuum has no mass, so it's difficult to say that photons aren't matter. Of course, it's also semantically unimportant to distinguish between matter and energy at all.
analyzing gravity waves would be a very fun thing to have my computer doing!
:P
Where else will you find "computer, "analysing gravity waves," and "fun" in the same sentence?
Not that that's a bad thing.
This theory states that no matter how hard it tries, the cat will never be able to catch a moving laser.
This theory states that no matter how large the warning on the side of the laser, someone will inevitably see what happens when they shine it in their eye.[1]
Shine a laser through a donut and one can theoretically throw a policeman into a brain lock as they try to defend themselves from the obvious sniper while also try to obtain the donut
See number 1, substituting 'stupid person' for 'cat'.
This theory states that, whoa, dude, when you shine the laser up your nose, it glows like Rudolph, man! *puff*[2]
This theory states that sharks with frickin' laser beams on their heads are more deadly than mutated sea-bass.[3]
And yes, I want one of these in pen form.
[1] They go blind
[2] I in no way condone the use of illegal drugs
[3] Being conducted in conjunction with the Darwin Society.
I guess I should prefix this with "I am not a physicist, but..."
Consider this quote from the article:
However, small earthquakes, acoustic noises and laser fluctuations can cause a disturbance at one site that could lead scientists to believe they have detected a gravity wave.
Now recall that Hanford was one of the nation's big plutonium production sites back in the day. There's still alot of waste around the site. It is also near a river (acoustic noise).
Certainly these factors are probably much less significant than, say, earthquake-prone California. But if I were tasked with selecting a site, I think I'd prefer somewhere flat and boring. The less disturbances the better. Like I said, though, I'm not a physicist, so perhaps they feel that they can compensate for these factors.
Best regards,
SEAL
I once had a degree in Physics and some knowledge of the subject. Now all I've got is the degree. Any better informed physicists want to take a shot at this?
Einstein described gravity in terms of warped space/time, and the motion of particles through it as the shortest possible path through a curved space. His numbers worked (confirmed as early as the 1920's if I recall) so folks mostly bought it. Einstein hoped to express all forces as some form of curve in space, but that didn't work out for him - other forces are selective in their effects, while gravity happens to everybody.
Now, these days we tend to view things in terms of particles. The reasons are less experimental than logical. We're not talking about tiny billiard balls hurling through space, quantum mechanical particles are a little too weird for that.
Take the following well established notions:
1- Energy does not exist apart from a mass (or alternately that mass and energy are the same thing - the two statements are pretty much the same.)
2- Vacuum has no mass - it isn't a medium that can carry energy.
3- Gravity, like the other three forces, transports energy.
Given these three, we pretty much must conclude that gravity is transported by particles. It might be a particle which, like the photon, has zero rest mass, but if energy is moving through empty space, a particle, by definition, must be carrying it.
Of course, saying so doesn't answer any questions at all. Why should the action of gravity particles distort space/time? If you have a good answer and experimental data to back it up, the Nobel committee has a sizeable cash prize waiting for you.
The structure of space-time itself. It's not the ether, since electromagnetism propagation is different.
...phil
...phil
"For a list of the ways which technology has failed to improve our quality of life, press 3."
No, the gravity waves from a passing bus or 747 are actually very small, even by LIGO's standards. However, the shaking of the earth due to seismic activity or a bus (passing very close to a detector) will be detectable. Fortunately, it's easy to model a passing bus, seismic activity can be characterized, and there is a small but significant range in which gravity waves from coallscing compact objects could be detected.
I did neglect to consider things like quantum interference, which in principle would make a difference. It would be hard to measure though unless the experiment was designed to look for it.
As far as I recall, general relativity defines gravity as the curvature of space-time. Gravity waves are the result of changes in the curvature of space time. Gravity waves are theorised have these properties:
Gravity waves will be accompanied by gravitons, a hypothetical particle that has zero rest mass and twice the spin of a photon.
Gravity waves and gravitons propagate outward at the speed of light.
Gravity waves compress mass in one direction perpendicular to the direction they travel, and expand it in a direction perpendicular to both the direction of compression and direction of travel.
Gravity waves are moving ripples in space-time.
Black holes coliding make big gravity waves.
Gravity waves pass through matter.
This experiment it is trying to get empirical evidence on all of the above claims. This has been a goal of some physicists since the theory was proposed in 1916. However, this goal has previously been beyond experimenters technological reach. It takes today's most sophisticated lasers and detectors to isolate a gravity wave from far away. Any local vibrations reaching either the lasers (like noise, or earthquakes) or the detectors will be easily confused with gravity waves. However, the mass of nearby objects does not interfere, just the vibrations they produce.
As for the design of the installation: it is in the shape of an L, because (as I mentioned before) gravity waves both compress and expand matter as they pass through it. On laser moves faster, and the other slower. This is different from a Michalson inferometer, which checks if normal gravity (that is: curvature of space-time) bends light. A Michalson inferometer isn't used to determine the nature of gravity waves.
Gravity affects all of the universe simultaneously (although it doesn't affect it much, it does affect it). Gravity waves are held back by the speed of light limit though. So, the two installations would get waves at different times, depending on the orientation of the earth to the event.
Of course, this is all conjecture, and that's why we US taxpayers get this installation. If this had already been proven, we wouldn't need these two new observatories.
PS: Check out the observatories homepage for more info!
Yes, I'm still a junky. Are you still a bitch?
Indeed. Tell your congresspeople to support LISA, a similar experiment, but to be done in space. The improved sensitivy (mainly from being off the earth) will allow many more scientific discoveries and very interesting astrophysics.
http://ligo.caltech.edu
Caltech's Press Release
I don't know why their writing articles on this now. LIGO has been in the works for quite a while now.
Just to give you an idea of how sensitive these things are: my roommate spent the summer working on calculating shifts in the earth's crust caused by the sun and moon, so that the correction factors can be applied. If I remember correctly, at one point Kip Thorne (the Feynman Professor of Physics here at Caltech) was working on correcting for the change in Earth's momentum caused by raindrops hitting the surface.
-ElJefe
Gravity waves move at the speed of light just like excitations of any other "massless field" (The field is the local geometry of spacetime itself). This "speed limit" is in fact necessary for the theory to be relativistic in the first place (i.e. not having a preferred frame of reference). The principle of (special) relativity o.t.o.h. is really well established, if gravity would violate it, we would most probably have seen the effects already (for example, in the original Michelson experiment which failed to find any velocity of the Earth w.r.t. the so-called "aether", which would have been a preferred frame, at any time of the year).
Since gravity waves are a feature of any field theory of gravitation, such as GR, they had better be found or not only would GR be ruled out but also any theory of gravity based on our understanding of classical and quantum field theory. Although for LIGO to detect it, the waves will have to be pretty strong (some not-too far supernova for example might do). Next-generation experiments are expected to be able to detect waves that originate from more common sources such as close binaries (mentioned in an earlier post).
On a more fundamental note, you never prove a scientific theory, you only (try to) disprove (falsify) it. In Einstein's words, "no amount of experimentation can ever prove me right, but a single experiment can prove me wrong."
Well, your point of view is one reason to do the experiment. A small minority of scientists still don't beleive in gravity waves. Therefore we look and see who is right. Michelson-Morley had much lower sensitivities.
However, a humougous majority of scientists beleive that space time itself is being distorted in a quaesi periodic way and that this is at least theoretically observable.
The whole reason why we talk about forces as being particles is that particles can move through a vacuum. Electromagnetism works across a vacuum because the force is carried by a particle: the photon. Radio waves do not need a medium to travel in because they are composed of photons.
"Gravitons" are what gravity particles are called. In principle, it works the same as radio, except with a different particle. Of course, there are important (and unexplained) differences between radio and gravity - that's what keeps physicists employed.
pork belly
pork barrel
we clear?
All the way to my quantum mechanics final exam.
:^)
I can't even remember where to begin to calculate the photon density in the field. If I did, I might be able to work that half out (although I'd probably get the wrong answer - seem to recall not doing that well on my quantum final either.)
The interference from a field that's parallel to the beam sure as hell won't be much. Of course at the edges it won't be parallel... I think I'll need some extra paper.
Thank God I quit physics.
Alcubierre's homepage (http://www.astro.cf.ac.u k/pub/Miguel.Alcubierre/index.html) has a broken link to the paper itself. I can't find another copy.
The New Scientist has an article about it here.
The warp paper mentioned in my other post is at
d _364000/364496.stm
http://www.lysator.liu.se/~nisse/doc/alcubierre/
Also there is a news article mentioning some of the ideas at
http://news.bbc.co.uk/hi/english/sci/tech/newsi
One thing I find interesting by this fact, is that since gravitational waves travel at the speed of light, space therefore has an elasticity.
For example, if a huge black hole were to open up where the sun is, and engulf it, the Earth wouldn't feel the effects of it for 7 minutes (I think its 7 minutes at c to the Sun?). I find that pretty cool.
guess you're too smart for us. what with our 'research' and all. we'll just let you take the helm now.
For people interested in tests of general relativity...
Gravity Probe B is a satellite that will be launched in a few years' time. It plans to check for one untested prediction of general relativity (the frame-dragging effect of massive spinning objects like the earth) by placing several hyperaccurate gyroscopes in orbit and measuring the change in the rotation axis of those gyroscopes from this effect.
It's been under works for 30 years now... here's the website for the project.
The whole system has to be incredibly accurate... I worked with this over the summer, and the technical details are scary (for example, the gyros used are the smoothest spheres ever made by man... if they were expanded to the size of the earth, the greatest height difference between valleys and peaks would be about 16 ft)
Thy're going to take an object and multiply it by the square of the speed of light to get some energy?
Jay (=
Comparatively, swampland is a GREAT place to put one of these things...
-jacob
I have always wondered what people who say things like this must think of scientists. Is the idea that at the research labs, PhD's sit around the bong taking hits and saying things like, "Whoa... dude... what if the universe, like, is the result of this huge explosion where there were all these particles and anti-particles and stuff? That would be awesome. Somebody start writing: I feel a paper coming on."
Differing scientific opinion, based on facts, is certainly incredibly important to scientific reasoning. Differing scientific opinion in the absence of facts is just annoying.
-jacob
You slam "these scientists" for thinking "too small," yet here you are making a world of half-witted judgements. But the irony is likely lost on you.
"START" reads "the first observable event";
"END" reads "the last observable event."
There are no assumptions about what comes "before" and "after," or what this even means in a human sense. It is undefined because we cannot (yet) know. This is very different from START being the absolute beginning of all things.
Physicists are (surprisingly?) flexible about the nature of the universe..
And I do believe that the Big Band theory is correct; it is simply not whole. The process earth inside of the shell has defined the shell as being the universe -- completely without understanding and beyond the fact that the platform exists, sitting on someone's desk, inside of a corporate network on some strange world.
Gosh, I hope we are on something like LINUX or Open Source. I would be really embarrassed if we were being run on a Windows system. I am getting nervous about a universal abend here.
Damn it Jesse, stop thinking!
it'll give us a chance to escape...
:-s
+&x
As you might imagine, the major obstacle to LISA is the expense of the thing. I suspect that the success (or lack thereof) of LIGO will have a big impact on whether LISA ever gets funded. However, all the signals that we know are out there (coalescing neutron stars and the like) are likely to be too weak to detect with LIGO I (only the most optimistic estimates give an appreciable event rate with LIGO I). If LIGO II gets funded, then it will almost certainly see some events, and that could renew interest in LISA. LIGO II isn't scheduled to begin installation until 2004 (assuming it gets funded at all), so I expect we won't see a space-based gravitational wave observatory until sometime after then.
-r
Seriously, though....
If they were to find that there were some frame-dragging effects, wouldn't this throw a humongous monkey wrench into the whole 'there is no aether' thing?
The way I was taught, *There was no "aether"*
To me, any indication of reference frame dragging would indicate otherwise. Maybe not *exactly* the same thing that the MM experiement "disproves", but still.....
Blech. Signatures.
I'm kind of surprised that they left out the whole reason for producing LIGO. Its primary purpose is not to prove that gravitational waves exist. We're pretty darn sure of that already. The stated goal of LIGO is to devise a way to make a gravitational wave "telescope". The idea is that you can cross index electromagnetic phemonema with gravitational waves and build up a database of types of celestial events, eventually to the point where you can tell what was happening on the other side of the galaxy without searching for electromagnetic signs. Because gravitational waves can pass through objects relatively uneffected, they have the potential to make observations of phenomena that are farther than our telescopes can reach or that are interfered with by other events. Check out www.ligo.caltech.edu/ to get it straight from the horse's mouth.
"I refuse to join any club that would have me as a member" - Groucho Marx
I didn't mean to imply LIGO was a bad idea. I'm glad LIGO is being funded, and hope LISA will be funded similarly. I'm not involved with either, but I've heard people who are say the pricetag on LISA might actually be less than for LIGO. I suspect that is due in large part to the fact that LIGO has already developed lots of the technology they would need for LISA. Personally, I'm skepitcal that LISA would be as cheap as advertised, but the scientific possibilities more than make up for that.
Y'all should know, though, that the next generations of LIGO are already "in the slot", and they promise to increase the event rates quite a bit. The whole trick is to isolate the mirrors as much as possible from disturbances that aren't gravity waves. Fortunately, there are very clever people working on the problem as we speak.
BTW...perhaps the best isolation would be to shoot the whole Michelson interferometer mess up into orbit. I'm pretty sure that some guys at NASA are working on this too. It's worthwhile to check out the LIGO page. Set
He said something about it, like he doesn't want to work on a big government funded project or something. So he's doing superstring theory now and little things that give the rest of us nosebleeds. On the plus side, if I were a phys major I could take a class from him. :)
Here's the link to another group doing research in this field:
http://www.cf.ac.uk/socsi/gravwave/index.html
And here's a quick overview of the timeline of this field of research:
http://www.gsu.edu/other/timeline/gravity.html
Beware of Wight Supremacists!
From what I hear:
The facility has a fence at a fairly large distance away. Not because of the sensitivity of the experiment though, but to cut down on the number of bullets entering the facility. Yup, locals apparently can't tell the difference between a building and an animal. Or maybe they were shooting at animals (humans are too). Or are they just really bad shots? No, wait! It gets better! I'm in the cafe and there's this guy telling me about some eerie government facility that seems to be top secret, hush hush and all that. On and on he goes with conspiracy theory...
Suddenly he identifies the facility (by location)- you guessed it - LIGO. (He didn't know the name)
Apparently the fence is what aroused suspicion among the locals.
Hey, I have a sense of humor.
Down here in Louisiana, we like to pass a good time, so I'll let that remark slide. But we also like to work hard, whether it is on a backhoe (yeah, I've done that) or detecting gravity waves (I'm going to the dedication today, just down the road).
And as a proud citizen of Louisiana, I challenge your lamer ass to a game of Dune2000. Weenie.
"Classic UFO's
A CRT doesn't shoot light, it shoots Cathode Rays otherwise known as electrons. These, unlike photons do have an electrical charge.
---CONFLICT!!---
Just a guess, but setting up a tunnel on the order of a kilometer deep or up would be pretty tough.
Also with multiple detectors on the earth this is quite easily accomplished and may already be incorporated into the current plan.
Wow I got to post.
Lou
Of course. A magnetic field has energy, which is the same as mass under relativity, and anything which has mass produces a gravitational field. And light does get deflected by gravitational fields. This is utterly negligible, of course, but then, so are the quantum interferences.